1. Field of the Invention
The present invention relates to a communication network such as the public switched telephone network (PSTN) wherein call processing is carried out to allow local number portability among numbers ported or moved between an original switching node and another switching node and to allow subscribers within the communication network to maintain a particular telephone or similar network access number regardless of number relocation or porting within the communications network.
2. Description of the Related Art
In recent years there has been much discussion and effort to establish methodologies, systems and solutions to the numerous issues pertaining to station number portability or local area number portability. While many people agree that the central goal of local number portability is the provision of a local (geographic) number to a network subscriber that stays the same regardless of physical network, those same people have often disagreed as to a particular solution to the local number portability problem. Moreover, it is the fact that the public switched telephone network (PSTN) is a "legacy system" that exacerbates the issues pertaining to the provision of local number portability.
As such, many approaches have been proposed for providing local number portability. Some of these approaches typically have been concerned with providing "switch-wide" call routing solutions or other solutions wherein a network routing address is derived from or is numerically related to an originally dialed number. For example, some solutions have proposed elaborate plans that require transforming numbers from one dialing plan to another dialing plan, performing sophisticated mapping operations in relation to the transformed numbers and then performing routing that requires changes to existing switching and routing infrastructures.
With switch-wide solutions to providing local area number portability, for example, call processing and routing are achieved by routing a ported call to a particular end office system (e.g., a switching centers) for final call routing within that end office system.
One such switch-wide local number portability solution has been offered by AT&T which is disclosed in U.S. Pat. No. 4,754,479 to Bicknell, et al. filed Sep. 17, 1986, issued Jun. 28, 1988 and entitled "STATION NUMBER PORTABILITY." In particular, the '479 patent discloses a system where a station number portability arrangement is provided that allows a subscriber who is ported from an original switch to a new switch to retain his or her originally assigned number regardless of any numbering plan constraints. Moreover, the system of the '479 patent requires certain portability assumptions including that all switches that are capable of porting must be within a single portability cluster, that calls are to be routed to a particular destination switch and that the destination switch is capable of performing certain database operations to ultimately route a call to a particular line.
A system of the type described in the '479 patent has certain drawbacks including a course granularity in terms of ultimate line particularity (i.e., only switch-wide porting is possible as opposed to line-specific porting) and a requirement that each destination switch must be capable of performing certain database operations to perform a subsequent line-specific routing.